Major changes are occurring, especially regarding memory usage (and security bugs, so I seriously suggest you upgrade). Your main gripe is there isn't very many of them at each release, since they have changed development style. This kind of development style is what I'd call rolling release, "ship changes when they are ready", instead of the usual "ship changes in the next version". The classic version numbering fails with this kind of development style, since the differences between major/minor start to fall apart. Look at something like the linux kernel, which follows a rather similar system. Every new version adds major features, just not very many, but they build up over time. In fact, the major-minor meaning was so useless Linus could just change the version from 2.6 to 3 without any significant changes.
As a gentoo user, I would expect you to be very familiar with the rolling release paradigm. Personally I think it works well for something like Firefox. I'm pretty sure I'm getting way more major features per unit of time now then before, since the waiting time between releases was so long. There are definitely some disadvantages to this approach though, but the advantages are worth it.